Type 1 diabetes mellitus, also termed insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease that specifically targets the pancreatic beta cells of the islets of Langerhans in a T-lymphocyte-mediated destruction. While insulin replacement therapy corrects the hyperglycemia, it is not a cure, since most IDDM patients eventually succumb to the complications associated with imprecise glucose homeostasis. One approach that can restore tight glycemic control is the replacement of beta cells in the form of islet allografts or xenografts. The latter may not become a clinical reality anytime soon primarily because of concerns for zoonoses. Allografts are ethically acceptable, yet they face both alloimmune rejection as well as autoimmune destruction following transplantation. It appears that three distinct death effector pathways are responsible for beta cell destruction: 1) Fas, 2) tumor necrosis factor alpha and 3) perforin/granzyme B. Similar to autoimmune destruction, it appears that Fas, TNFa and perforin/granzyme B are important death effectors in allograft rejection of islets. Genetic engineering of islets to produce inhibitors of these pathways may facilitate allogeneic islet transplantation and may result in long-term survival. In the non-obese diabetic (NOD) mouse model, engineering islets ex vivo to express a variety of immunoregulatory cytokines and proteins has resulted in significant, but not indefinite, prolongation of allogeneic islet transplant survival. One important reason why long-term or indefinite allograft survival has not been achieved is the nature of the gene delivery vectors, most of which are of viral origin and highly immunogenic or toxic to islet cells. Recent engineering of lentiviruses including human immunodeficiency virus (HIV-1), feline immunodeficiency (FIV) and equine infectious anemia viruses (EIAV), has resulted in vectors that are able to infect non-dividing cells, are non-immunogenic in vivo and can stably integrate into the host cell. These desirable characteristics of lentiviral vectors as gene delivery vehicles for islets ex vivo, are in contrast to the highly immunogenic, transient and toxic nature of vectors that have been recently used in islet gene transfer strategies (adenovirus, herpes simplex). While HIV-based lentiviral vectors have been demonstrated to readily infect human islets, the nature of the virus strain is a significant impediment for clinical applications. EIAV, on the other hand, offers the same characteristics as HIV and is not pathogenic in humans. The focus of this proposal is to demonstrate that soluble antagonists of Fas, TNF and granzyme B can protect islets in culture from apoptosis activation and to further develop the EIAV lentiviral system as an efficient gene delivery vector of cDNAs encoding inhibitors of Fas, TNFa and perforin/granzyme B-dependent death effector pathways, alone or in combinations. This may be a desirable approach to facilitate allogeneic islet transplantation as a possible therapy for IDDM.